1. Field of the Invention
The present invention relates generally to a hydraulic breaker. More particularly, the present invention relates to an improvement of the hydraulic breaker wherein a piston is dynamically displaced in upward and downward directions by hydraulic pressure, and nitrogen gas pressure the piston imparts a large striking force on a chisel disposed below the piston so as to break a substance, e.g., a rock, a concrete block or the like, at the end of a downward stroke of the piston.
2. Description of the Related Art
Conventional hydraulic breakers are of two basic designs. One, a hydraulically driven type wherein a piston is driven directly by hydraulic pressure, and two a gas or spring intervention type wherein nitrogen gas or a spring is forced into a compressed state in a cylinder by the upward movement of the piston and then expands and imparts a large striking force to a chisel. Both types of conventional hydraulic breaker are equipped with accumulators for the hydraulic pipings on the high pressure side located on the oil feed side. In addition, breakers are equipped with accumulators for pipings on the low pressure side located on the oil discharge side, the purpose of the accumulators is to prevent pressure pulsation in the pipings. However, it has been found that the accumulators often malfunction due to leakage of gas. For this reason, it is necessary to inspect and replace accumulators often. Therefore, the conventional hydraulic breaker has problems that lead to high maintenance costs and low operating efficiencies. Additionally, hydraulic breakers with accumulators are expensive to manufacture. In view of the foregoing problems, some solutions have been attempted such that a constant quantity of high pressure oil flows through hydraulic passages on the high pressure side and a constant quantity of low pressure oil likewise flows through hydraulic passage on the low pressure side during a step of upward displacement of the piston as well as a step of downward displacement of the piston for the purpose of eliminating a necessity for accumulators. In spite of the foregoing solutions, however, the main valve is complicated in structure and the piston is unavoidably designed to have a long length in operative association with a cylinder having a long sleeve. This leads to another problem of scratching of the piston and cylinder during sliding movement of the piston relative to the cylinder sleeve. One accumulator type conventional hydraulic breaker is disclosed in U.S. Pat. No. 4,817,737. According to this prior invention, the hydraulic breaker is constructed such that a second stage of the piston is dimensioned to have a diameter smaller than that of a fourth stage. With this design, however, the breaker cannot be assembled unless the cylinder sleeve is longer than the working stroke of the piston. The long cylinder sleeve increases the cost of manufacturing the breaker. In addition, because it is difficult to maintain, concentricity with respect to the cylinder and the piston using a long piston and cylinder, scratching of the piston and cylinder sleeve is more common. Another deficiency of the prior art is the arrangement of a nitrogen gas chamber directly above the upper high hydraulic pressure chamber. This leads to oil leaks from the high pressure chamber into the nitrogen chamber which causes the piston to incorrectly operate. A lost deficiency of the conventional breaker is that the piston is normally biased in the downward direction by high pressure, thus the operator can not raise up the chisel manually to the position where the piston starts its movement. Thus, it is difficult to perform a so-called chipping operation.
As previously explained, conventional hydraulic breakers suffer from the following deficiencies:
1) accumulators which are costly to manufacture and maintain;
2) main valve structure which is complicated and expensive to manufacture and maintain;
3) long piston and cylinder sleeve which is expensive to manufacture and is costly to maintain;
4) gas and oil chamber configurations which lead to oil leakage; and
5) inability to manually raise chisel to perform chipping operations.